By Mark Ollig
Recently,
yours truly attended the Mission to Mars presentation at the Fitzgerald Theater
in St. Paul.
John
Grotzinger, chief scientist of NASA’s Mars Curiosity mission, spoke for a
couple of hours before a capacity crowd.
The
event was moderated by Tom Weber of Minnesota Public Radio.
Curiosity
is the latest NASA rover traversing the surface of Mars after its highly
complex landing last August nicknamed, “Seven Minutes of Terror.”
It
takes seven minutes for the rover (attached to the descent stage inside of a
protective back shell capsule), to go from the top of the Martian atmosphere to
its surface.
Unlike
the Mars landings of rovers Opportunity and Spirit, each cushioned inside with
inflated airbags to protect them when they landed and bounced along the surface
until they stopped, the Curiosity landing was precisely controlled.
The
capsule containing the Curiosity rover detached from the rocket which brought
it from Earth, as it begins to enter the Martian upper atmosphere.
The
attached aeroshell heat shield is subjected to temperatures of up to 3,800
degrees Fahrenheit as it enters the atmosphere; however, inside the capsule, it
is a cool 50 degrees.
At
approximately 13 miles above the surface, the friction from Mars atmosphere
dramatically slows the capsule from 13,200 to 1,000 miles per hour.
At
the seven-mile point in its descent, a parachute opens.
This
parachute is the largest and strongest super-sonic parachute ever made.
Although
it only weighs 100 pounds, the parachute needs to withstand 65,000 pounds of
force.
The
capsule’s heat shield drops off when it’s about five miles from the surface.
Five
seconds go by and the capsule’s radar system activates. This determines its
speed and altitude, which is needed in order to calculate when to begin a
rocket-powered descent.
One
minute and 20 seconds from when the heat shield drops off, the capsule and its
connected parachute disconnect from the descent stage, and drift away.
This
leaves the descent stage and its precious connected cargo, Curiosity, in a free
fall, traveling towards the planet.
It’s
a mile above the surface, and descending at a speed of 170 miles per hour.
At
4,224 feet above the surface, eight retrorockets, attached to the descent
stage, fire. They maneuver the descent stage away from the falling empty
capsule and attached parachute in order to avoid any chance of collision.
Here
is where it gets complicated in the course of the landing.
NASA
calls this next sequence the Sky Crane maneuver.
John
Grotzinger jokingly called it, “Rover on a rope.”
Imagine
a huge sky crane lowering a steel beam from a skyscraper to the ground. The
steel beam in this example is the 2,000-pound Curiosity, being lowered by the
descent stage as it travels at only 1.7 miles per hour towards the Martian
surface, which is now roughly 490 feet away.
At
approximately 45 feet from the surface, four of the eight descent stage’s
retrorockets shut themselves off, as three 21-foot nylon ropes (supporting the
rover); along with an information-relaying “umbilical cord,” immediately spool
out from the descent stage, which is still connected to the rover vehicle.
At
25 feet from the surface, these nylon ropes slowly lower the Curiosity rover,
towards the surface of Mars.
Approximately
16 feet from the surface, and traveling at 1.3 miles per hour, Curiosity’s six
wheels and suspension system are lowered (like a commercial aircraft’s landing
gear prior to landing).
With
the nylon cables fully spooled out, the rover gently touches down onto the
surface of Mars while the four retrorockets are still firing.
The
descent stage sensors know the rover is now on the ground, because the weight
on the nylon cables has been drastically reduced.
The
nylon ropes, along with the umbilical cords disconnect from the rover.
The
ropes and umbilical are still connected to the descent stage, as it quickly
flies away and crashes (as planned) about 500 feet from the rover.
The
seven minutes of terror are over.
The
rover had safely landed on the surface of Mars, inside the 96-mile wide Gale
crater, which was formed during a meteor impact about 3.5 billion years ago.
This crater is thought to have held significant amounts of water in its past.
The
time here in Minnesota was 12:32 a.m. Aug. 6, 2012, and yes, I was watching
this event as it happened on NASA TV.
I
learned that over 500,000 lines of computer programming code were used during
this complicated landing.
According
to Adam Steltzner, an engineer at NASA’s Jet Propulsion Laboratory (JPL), the
successful landing was also “the result of reasoned engineering and thought.”
“Once
upon a time, Mars and Earth were very similar,” Grotzinger said during his talk
at the Fitzgerald Theater.
During
a press conference held March 12, NASA announced Curiosity had discovered proof
of past water on Mars.
“We
have found a habitable environment that is so benign and supportive of life,
that probably if this water was around, and you had been on the planet, you
would have been able to drink it,” Grotzinger said.
For
many of us in the Fitzgerald Theater, the big question we were waiting to have
answered was whether Curiosity could prove if there was actual life on Mars
during its past.
Be
sure to read next week’s Bits & Bytes for the conclusion of this column.
Oh,
and Randy – thank you very much for the tickets.
